Effect Of Adding Of MgB₂on The Oxidation Resistance Of Al₂O₃-C Refractories

Al2O3-C refractories have good corrosion resistance and thermal shock resistance,are widely used as slide gate plate in continuous casting,elongated service life of nozzle,submerged nozzle,stopper-monoblock and so on.However,carbon-containing refractories have one main shortcoming:it is susceptible to oxidation.That can lead to degradation of the refractories.To improve the oxidation resistance of carbon-containing refractories,antioxidants,such as metals(Al,Si),alloys(Mg-Al),and carbides(B4C,SiC) are often added to the refractories.However,these antioxidants have some drawbacks.For example,when aluminum contacts with carbon,it reacts with carbon to form Al4C3.The formation of Al4C3can be a problem,because Al4C3phase is easily hydrated,even at room temperature.The hydration of Al4C3will cause a large volume expansion and deterioration of the material during reheating.In consideration of the problem,it is necessary to develop new antioxidants for improving oxidation of Al2O3-C refractories.The oxidation resistance of Al2O3-C refractories with MgB2addition,the phase analysis and the micro-structures of the Al2O3-C refractories in high-temperature were investigated by means of oxidation test,x-ray diffraction (XRD),thermogravimetric analysis (TG),differential scanning calorimetry(DSC) and scanning electron microscope(SEM) observation assisted with energy dispersive x-ray analysis(EDXA).The oxidation resistance mechanism and the mechanical properties of MgB2added Al2O3-C refractories were discussed.Experimental results indicated that MgB2was found to react with CO gas firstly, to form MgO and B2O3.The formed MgO further reacts with Al2O3to form MgAl2O4.MgAl2O4enhances the combination of aggregate and matrix,and the apparent porosity was reduced. At the same time,B2O3reacts with Al2O3to form Al18B4O33and a li q u id ph a se. A l18B4O33c o ve re s on th e su rf a ce of th e carb o n,p r e v en ts A l2O3-C ma te r ia lf r o m o x id a ti o n. T he li q u i d ph a se f il l i n g th e po r e s ma k e s th e m a t e r ia l mo r ed e n se r. T h u s, M g A l2O4, A l18B4O33a n d th e li q ui d p h ase in hi b i ts ox id a ti o n o f t he A l2O3-Cr e f ra c to r ie s. By th e st u d y o f me ch an ic a l p ro p er ti e s, it in d ic a te d th a t th e st r e n gt h o fsa mp le w it h Mg B2a d d it i o n w a s h ig h er th an th a t o f c o mm o n a dd i t i v e s. T h e r e su l t me a n sMg A l2O4a nd A l18B4O33h a v e a p o si t i v e in f lu e n c e o n t he s t r e n g t h of A l2O3-Cr e f ra c to r ie s.